Primary – Hints and tipsResource
- When working with plants, pupils and teachers should always wash their hands after handling plants (including seeds), soils, composts, manures, equipment and other related materials.
- Plants (and parts of plants) can be poisonous, cause allergic reactions in some people or may have been treated with chemicals (such as pesticides).
- It is particularly important that pupils understand that they must never eat plants found in the wild or in the school grounds, unless given instructions that they may do so.
- Please remember that wild flowers should not be picked and it is illegal for anyone (without the permission of the owner or occupier) to uproot any wild plant.
Soil mix and a note about ‘compost’
For growing plants in film pots, use any good quality multipurpose potting compost. Mix the compost 50 : 50 with fine grade vermiculite to help retain moisture (but this is not essential).
Wherever possible, use a peat-free compost as this encourages awareness of environmental concerns. However, when investigating the effect of adding different amounts of fertiliser, it is necessary to use a compost that is low in mineral salts, so here moss peat works well. Vermiculite on its own does not supply plants with enough physical support. For growing insectivorous plants, many thrive only on moss peat, but buy the minimum that you need.
There may be some confusion about the use of the term ‘compost’. The process of composting is used in many gardens as a way of decomposing waste plant material (including some household waste, such as vegetable peelings) and converting it into a soil-like material, known as compost (see, for example, OSMOSIS 18). The decomposition occurs as a result of microbial activity (mainly bacteria and fungi).
The resulting compost is a valuable material for use in the garden, supplying nutrients (in the form of mineral salts) and contributing to improved soil structure and texture. Gardeners also use prepared ‘composts’ for growing seeds and plants, particularly during their young stages.
These prepared ‘potting composts’ are made up of various mixtures of loam or peat, with sand or grit and added nutrients. They are sieved to provide a fine and uniform texture and sterilised to remove weed seeds. For this booklet, we have adopted the neutral term ‘soil mix’ to avoid confusion with different types of composts and other growing materials.
Fertiliser pellets (e.g. Osmocote®) consist of a water-soluble granule containing a mixture of nitrogen, phosphorus and potassium (often abbreviated NPK) in the right balance to supply the necessary mineral salts and promote healthy growth in plants. Each pellet is coated with a thin layer of resin, which controls the release of nutrients.
Several kinds of capillary matting are available, with different textures and weights. Lightweight types are preferable for use in the classroom. Capillary matting may seem relatively expensive, but it can be re-used several times). Wash the matting carefully and soak it in a very dilute sterilising solution, prepared from sterilising tablets used for babies’ feeding bottles. Rinse thoroughly before using it again.
Film pots – for growing seeds
These are available from photographic and camera shops, and chemist shops where films are processed. They may become scarcer as digital photography progresses, but they are still available at the time of writing (2007). They can be re-used many times. The advantages of using film pots are that each child can have their own pot and watch their plant grow, they require only small quantities of soil mix or other materials, they occupy only a small space in the classroom and are easy to clean.
There are plenty of other pots or containers that can be used, including yoghurt pots or small plastic flower pots.
Some notes on seeds and suitable plants to grow for investigations in the classroom
For very young children, it is best to use large seeds, which are easy for them to handle. Suitable examples are peas, beans, sunflower and sweet corn. Other seeds that are good for growing in the classroom and using in investigations include mustard, cress, mung bean and wheat. Make sure that any seeds you use are within the sowing date.
Seeds may be dusted with fungicide and it is good practice to teach the children that they should never put seeds in their mouth and must always wash their hands after handling seeds.
The sugar Snap Pea
The life cycle of a sugar snap pea and how to grow it are described in ‘Parts of a plant and their functions’. For younger children, it is an ideal plant to grow because the seeds are large enough for children to handle and the life cycle is relatively short. Seeds sown in March produce flowers in June and edible peas would be produced by the
end of the summer term (July). It can be grown out of doors or in the classroom.
Using Radishes in Investigations
The radish (Raphanus sativus) is a useful plant for carrying out simple investigations (for example, see page 28). The seed is inexpensive and widely available. Seeds in a single packet show relatively little genetic variation, compared with some other plants. This means that when comparisons are made, differences are likely to be due to the experimental conditions rather than variation between the seeds. They can be grown successfully in film pots. Radish plants are small and compact and, if grown under a light bank, can give a ‘crop’ within three to four weeks. This crop can then be measured in a variety of ways.
Rapid-cycling Brassicas are small plants and take up relatively little space. They produce flowers within two to three weeks and ripe seeds within 5 weeks. Rapid-cycling Brassicas are also known as ‘fast plants’. These ‘fast plants’ have become a very useful teaching resource for a number of other reasons. The plants can be used to illustrate all stages of the life cycle and, because of the short timescale, the children’s interest can be maintained. The plants need to be cross-pollinated and children can be involved in doing this.
Note that rapid-cycling Brassicas need to be grown under a light bank (see page 14). Seed is available from Blades Biological Ltd (www.blades-bio.co.uk) or from Philip Harris (www.philipharris.co.uk).
Understanding Respiration and Photosynthesis
Strictly, neither of these words appears on the curriculum for children at this level. However, indirect reference is likely to be made to both processes, so we give these background notes in a way that could be used with children. These are not easy concepts at this level, but it is very important that a suitable approach is adopted and so avoid misconceptions that occur all too frequently at later stages in the study of science (and biology in particular). Teachers may also wish to refer to the General note on ‘Food in plants’ in the Parts of a plant and their functions booklet.
First, it is important to establish that both processes are unique to living organisms. Both processes are concerned with energy; both processes are involved with the exchange of two gases (oxygen and carbon dioxide) and both processes are part of the carbon cycle.
We look at each process in turn, but remember it’s all to do with energy, oxygen and carbon dioxide. Children should also understand that in science, we link ‘food’ primarily with it being a source of energy.
Respiration = the way that energy is released from food
Respiration occurs in ALL living organisms ALL the time. When an organism stops respiring, it is no longer alive. Respiration uses food molecules (usually glucose) and releases energy from them. Respiration usually requires oxygen to do this and gives off carbon dioxide. Remember that plants as well as animals carry out respiration and don’t confuse ‘respiration’ with ‘breathing’ (see extra notes below).
Photosynthesis = the way plants use energy to make food
Photosynthesis occurs ONLY in green plants (and some simple organisms that contain pigments similar to chlorophyll) and ONLY when there is light. The green pigment (chlorophyll) traps the energy in the (sun)light and then uses this energy to build up certain carbohydrates (including glucose). The process of photosynthesis uses carbon dioxide from the air and water inside the plant to make this glucose. The process gives off oxygen and this passes out of the plant into the air. The glucose is the ‘food’ that has been made and it can then be converted into other substances in the plant (including proteins, fats and other carbohydrates).
Look at the words: photo + synthesis (light + building up); carbo + hydrate (carbon dioxide + water).
Some extra notes
1. The energy released is used in different ways by the living organism – for living processes, moving around, keeping warm, growing, making new substances.
2. People often get confused with ‘breathing’ and ‘respiration’ and use the words as if they mean the same thing. Make sure the children understand that in humans, ‘breathing’ is the way we fill our lungs with air (and so get oxygen into the body) then empty the lungs (and so get rid of the carbon dioxide that has been produced). Plants also need a supply of oxygen and to get rid of carbon dioxide, but the gases pass in and out of the leaf (or other parts of the plant) without any special breathing movements.
1. Chlorophyll is the green pigment in plants. Other pigments can trap light energy, and this energy can also contribute to photosynthesis. Some leaves look red because another pigment obscures the green chlorophyll, but the chlorophyll is still there and can trap the light energy for photosynthesis.
2. There is plenty of water already inside the cells of a plant, so the plant does not take in extra water just for photosynthesis.
Gases in and out of a plant – Let’s look more closely at what happens to the gasses involved in photosynthesis in a (green) leaf of a plant. Remember, respiration is going on all the time, so the leaf is using oxygen and giving off carbon dioxide. If it is a bright sunny day, photosynthesis is occurring at the same time. This means the net effect is that the leaf uses carbon dioxide and gives off oxygen.
So it probably uses up the carbon dioxide (already inside the leaf) given off from respiration and then takes in more from the air outside the leaf. Similarly, some of the oxygen (from photosynthesis) is used by the plant for respiration and any extra oxygen passes out of the leaf into the air.
Energy capture and release – The process of photosynthesis captures energy in light and converts it into a form that can then be built into food substances. The substances in the plant formed by this process (such as glucose and other carbohydrates) now contain this energy, which is then released in the process of respiration.